1. Field of the Invention
This invention relates to an electromagnetic clutch for use in a compressor for an automotive air conditioning system, and more particularly to an electromagnetic clutch that includes an apparatus for preventing permanent heat damage to the clutch.
2. Description of the Prior Art
Generally, a compressor for an automotive air conditioning system is driven by the engine and its operation is controlled by an electromagnetic clutch. If the rotating motion of the compressor is suddenly stopped, e.g., by locking of the wraps, the compressor should be quickly disconnected from the engine. Since the compressor may be driven by a belt which also drives other equipment such as an alternator, etc., it is necessary that the movement of the other equipment is not effected when the compressor is stopped.
Furthermore, if the rotation of the compressor is suddenly stopped and the electromagnetic clutch is still engaged to drive the compressor, a sliding frictional contact is created between the rotor and the armature plate of the electromagnetic clutch. Frictional heat is generated by this sliding frictional contact, which can cause the seizure of the rotor and armature plate. The bearing which rotatably supports the rotor may also be damaged by such frictional heat. It is therefore desirable to quickly disengage the electromagnetic clutch and to prevent the clutch from being reengaged until the compressor has been repaired.
One possible solution to resolve the above noted problems is to use a temperature fuse. A temperature fuse is disposed on the rotor of the electromagnetic clutch adjacent to the frictional surface of the rotor and armature plate and stops the operation of the clutch by melting itself.
However, it is impossible to directly dispose a temperature fuse on the frictional surface of a rotor, and therefore there is a large difference between the actual temperature on the frictional surface of the rotor and the temperatures detected by the fuse. Thus, a temperature fuse is not able to precisely control the operation of an electromagnetic clutch in response to the temperature of a frictional surface of the rotor. Also, since the temperature fuse is placed on the outer portion of the compressor, the temperature fuse may detect the heating of the compressor and unnecessarily cease the operation of the electromagnetic clutch.
Furthermore, since a temperature fuse will cease the operation of the clutch by melting itself, it is necessary to replace the fuse in order to again use the electromagnetic clutch. Since the temperature fuse is normally disposed within the hollow space of the rotor, it is necessary to remove the clutch from the compressor to replace the fuse, complicating maintenance of the clutch.